Aliphatic glycosides have been known for at least sixty years. They are nonionic surfactants with low toxicity and gentleness to the skin. They can be made from renewable resources and are rapidly degraded in the environment.
In spite of the excellent properties of the aliphatic glycosides, they have not achieved great commercial acceptance because of the difficulties encountered in their production. Rohm & Haas Corporation has been providing alkyl glycosides in which the alkyl group is formed from a mixture of fatty alcohols having 8 and 10 carbon atoms. The compositions were sold under the trade name BG-10 and CG-110. The BG-10 composition is a dark, almost black, material and is used only in commercial formulations. The CG-110 material is a light colored product having a dissolved solids content of about 70%, which is useful for consumer applications.
Early processes for the preparation of aliphatic glycosides were two-step processes. The first step comprised the reaction of a lower alcohol having 1 to 6 carbon atoms with a source of saccharide in the presence of an acid catalyst to form the aliphatic glycoside. These aliphatic glycosides do not have useful surfactant properties. Since water is miscible with, or highly soluble in, the alcohols, the reaction mixture can contain substantial quantities of water (see U.S. Pat. No. 4,721,780). The higher aliphatic glycosides in which the aliphatic group contains from 7 to 22 carbon atoms, were prepared by transacetalization of the lower glycosides with higher fatty alcohols under substantially anhydrous conditions.
More recently, aliphatic glycosides having alkyl groups with from 7 to about 22 carbon atoms have been prepared by a "direct process". In the "direct process" a long chain fatty alcohol is reacted with a source of saccharide in the presence of an acid catalyst under conditions in which the water formed in the reaction is removed as quickly as it is formed to maintain the water content of the reaction mixture at as low a level as is reasonably possible. The water formed in the reaction is only slightly soluble in the fatty alcohol and any undissolved water results in the rapid formation of unwanted byproducts. The parameters of the "direct process" were set out in U.S. Pat. No. 3,839,318, which is incorporated herein by reference. Other patents such as U.S. Pat. Nos. 4,939,245, 4,950,743 and 5,003,057 also describe the "direct process" and are incorporated herein by reference.
The references disclose use of an anhydrous source of saccharide or mixing a hydrous saccharide source with an alcohol, present in stoichiometric excess, and heating the mixture under reduced pressure to remove the water. An acid catalyst is added to the mixture of saccharide source and fatty alcohol after the water has been substantially eliminated and the mixture heated under reduced pressure to form the aliphatic glycoside (see Australian patent 272,247 and EP 132 046). German application 3 833 780.0 discloses forming a slurry of anhydrous saccharide and alcohol and adding the slurry to a heated second portion of alcohol.
It is preferred to use a hydrous saccharide source since hydrous saccharide sources are much less expensive than the anhydrous material.